This proposal investigates the role of an RNA-binding oncoprotein in mammary tumorigenesis. This protein is located in the cytoplasm and binds to insulin-like growth factor-ll, beta-actin, c-myc, and other mRNAs. We call it the c-myc Coding Region instability Determinant-binding Protein or CRD-BP. because it binds to an instability determinant in the c-myc mRNA coding region. The CRD-BP affects RNA translation, stability, and localization, depending on the RNA to which it binds. It is expressed abundantly in fetal tissues but is repressed shortly after birth. Therefore, it probably has a special role in fetal life. Three findings also link the CRD-BP to breast cancer: (a) The CRD-BP is undetectable in normal breast tissue but is present in ~60 percent of human breast tumors, (b) The CRD-BP gene is amplified in ~30 percent of human breast tumors, (c) The CRD-BP induces mammary adenocarcinomas in female transgenic mice. Three aims use transgenic mice to investigate the pathways of mammary tumor induction by this RNA-binding oncoprotein. Aim I. Determine if CRD-BP expression is required continuously to maintain an existing mammary tumor. Mammary tumors in transgenic mice continue to express the CRD-BP and thus might be CRD-BP- dependent for their survival. To investigate this idea, Aim I exploits a mouse model in which mammary- specific CRD-BP expression is induced by doxycycline (dox), a tetracycline analog. Mammary tumors are expected to arise in dox-treated mice. Aim I then asks: Do these tumors stop growing or regress when dox is withdrawn? Our working hypothesis is that tumors will regress when CRD-BP expression is repressed. Aim II. Use microarray analysis to compare gene expression profiles in non-neoplastic mammary tissues and in purified mammary epithelial cells of mice that do or do not express the CRD-BP. Some CRD- BP-regulated RNAs could play central roles in the induction and maintenance of mammary tumors. Aim III. Determine how genetic and environmental factors contribute to mammary tumorigenesis in CRD-BP-expressing mice. The goal is to assess how the tumor suppressor Ape and the chemical carcinogen N-ethyl-N-nitrosurea (ENU) affect CRD-BP-mediated tumor formation. We predict Ape deficiency and ENU treatment will synergize with the CRD-BP to increase tumor incidence and malignancy. Many of the well-studied oncoproteins are transcription factors or protein kinases. The CRD-BP is an unusual oncoprotein, because it resides in the cytoplasm and binds to RNA. By investigating the oncogenic properties of the CRD-BP, the RNAs it affects in vivo, and its interactions with tumor-inducing genetic and environmental factors, we hope to uncover novel tumorigenesis pathways. [unreadable] [unreadable] REVISED: October 27, 2005 (see Revision Note) [unreadable] [unreadable] [unreadable]